Issue While Deleting the Last Record

In the view top applet is based on "Opportunity" BC and the bottom applet
is based on "Activity" BC.

The requirement is, when I am deleting the records in the bottom applet
(Based on "Activity" BC) , in the top applet "DesCription" (Field in "Opportunity" BC)
field should be updated accordingly.

Assume that there is only one record in the bottom applet.
Here the problem is when I am deleting the record in the bottom applet, in the top applet "DesCription" field is not getting
updated accordingly.

On deletion of an activity, you need to check if there is any other activity exists or not and set a variable/field value. Based on this field value, set the description field with an appropriate value in the parent applet.